Lubricating Oil Composition and Method for Operating Automatic Transmission

ABSTRACT

A lubricating oil composition containing a bis-type alkenyl-substituted succinimide which is prepared by reaction of succinic anhydride substituted with 2-alkenyl group having a branched structure in β-position with alkylenepolyamine or a compound derived from the bis-type alkenyl-substituted succinimide by post-treatment in combination with a mixture of an overbased sulfonate having a C 20 -C 24  alkyl group and an overbased salicylate having a C 14 -C 18  alkyl group shows a high friction coefficient within a wide sliding velocity range and keeps its high anti-shudder performance for a long period of time.

This application claims priority to Japanese Patent Application number JP2011-021118 which was filed in Japan on 2-2-2011.

FIELD OF INVENTION

The present invention relates to a lubricating oil composition that shows a high friction coefficient in a wide sliding velocity range and keeps good anti-shudder performance for a long time of period. In particular, the invention relates to a lubricating oil composition valuable as a lubricating oil for automatic transmissions. The invention further relates to a method for operating an automatic transmission using the lubricating oil composition.

BACKGROUND OF INVENTION

Heretofore, an automatic transmission oil, that is, a lubricating oil for automatic transmissions, has been employed for assisting smooth operation of automatic transmissions equipped with a torque converter, gear mechanism, wet clutch and hydraulic system, such as automatic transmissions, continuously variable transmissions and dual clutch transmissions. For the recently developed automobiles, it is required to improve fuel economy. Therefore, the recently developed automobiles have been manufactured to have a less volume and a less weight. The automatic transmissions are also required to have a less volume and a less weight for the improvement of fuel economy. Thus developed small sized and light weight automatic transmissions require a lubricating oil showing improved friction performance such as higher friction coefficient. In addition, since automobiles equipped with an automatic transmission sometimes encounter vibration (that is referred to as “shudder”) when the automatic transmission operates, the lubricating oil is required to keep the shudder caused in the operation of the automatic transmission under a lower level for a sufficiently long period of time.

WO 97/14773 A1 discloses a lubricating fluid for power transmissions which contains an additive comprising an alkenyl-substituted succinimide that is prepared by reaction of a succinic anhydride substituted with an alkenyl group having a branch structure in a-position and polyamine. It is described that the addition of the additive enables to maintain good anti-shudder performance for a long period of time.

WO 97/14772 A1 discloses a lubricating oil composition containing an alkenyl-substituted succinimide that is prepared by reaction of a succinic anhydride substituted with an alkenyl group having a branch structure in a-position and an amine compound.

WO 2008/157467 A2 discloses novel pyrrolidine compounds and succinimide compound which are of value as friction modifiers for imparting excellent friction modifying performance to lubricating oil compositions without adverse effects on the viscosity properties of the lubricating oil composition at low temperatures.

Tribology online, 3, 6(2008), pp. 328-332 discloses results of studies of low molecular weight alkenylsuccinimides on anti-shudder performance. In the study, a number of low molecular weight alkenylsuccinimides and aliphatic amide compounds are tested. Examples of the low molecular weight alkenylsuccinimides include a bis-type alkenyl-substituted succinimide obtained by reaction of succinic anhydride which is substituted with 2-pentyl-2-tridecyl and an amine compound as well as a bis-type alkenyl-substituted succinimide obtained by reaction of succinic anhydride which is substituted with 2-hexyl-2-hexadecenyl and an amine compound.

SUMMARY OF INVENTION

One embodiment of the present invention is to provide a lubricating oil composition containing a novel friction modifier which is capable of imparting excellent friction modifying performances to the lubricating oil composition.

Another embodiment of the present invention is to provide a method for operating automatic transmissions using the lubricating oil composition.

In one aspect, the present invention provides a lubricating oil composition comprising a base oil having a lubricating viscosity and the following additives:

a friction modifier in an amount of 0.1 to 10 wt. %, a nitrogen-containing ashless dispersant in an amount of 0.05 to 10 wt. %,

a phosphorus compound in an amount of 0.1 to 10 wt. %, and

a metal-containing detergent in an amount of 0.005 to 4 wt. %,

in which the amounts of the additives are based on an amount of the lubricating oil composition,

the friction modifier is selected from the group consisting of

a friction modifier (A) comprising an alkenyl-substituted succinimide of the following formula (I) or a post-treated derivative thereof:

in which each of R₁ and R₁′ independently is an alkenyl group having a branched structure in β-position which is represented by the following formula (1), R₂ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 13 carbon atoms, or a 5-8 membered heterocyclic group, x is an integer of 1 to 6, and y is an integer of 0 to 20:

in which each of R₃ and R₄ is an aliphatic hydrocarbyl group and a total carbon atom number of R₃ an R₄ is in the range of 3 to 45, under the condition that a carbon atom number of R₃ is larger than a carbon atom number of R₄ by 3 or a carbon atom number of R₃ is smaller than a carbon atom number of R₄ by 1; and,

a friction modifier (B) which comprises an alkenyl-substituted succinimide of the following formula (11) or a post-treated derivative thereof:

in which each of R₁ and R₁′ independently is an alkenyl group having a branched structure in β-position which is derived from a dimer of a single linear α-olefin having 3 to 24 carbon atoms, and Q is a residue of an alkylene-polyamine having a 1 to 20 carbon atoms and containing an amino group at least at each terminal thereof, and

said metal-containing detergent is a mixture of an overbased sulfonate having an alkyl group containing 20-24 carbon atoms and an overbased salicylate having an alkyl group containing 14-18 carbon atoms in a weight ratio of 1:4 to 4:1.

The lubricating oil composition can contain the friction modifier (A) and friction modifier (B) in combination.

From another point, the present invention provides a method for operating automatic transmissions (specifically, automatic transmissions, continuously variable transmissions, and dual clutch transmissions) in the presence of the above-mentioned lubricating oil composition.

The lubricating oil composition provided by the invention is effective to impart improved friction performances such as an increased friction coefficient and a prolonged friction coefficient stability. Therefore, a lubricating oil composition containing the friction modifier of the invention can keep shuddering of an automatic transmission under a satisfactorily low level for a relatively long period of time.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the lubricating oil composition of the invention are described below.

(1) The friction modifier is the friction modifier (A), each of R₃ and R₄ in the formula (1) independently is a linear alkyl group, and the total carbon atom number contained in R₃ and R₄ is in the range of 13 to 21.

(2) In the formula (1), x is 2 and y is an integer of 1 to 3.

(3) In the formula (1), x is 2 and y is 1.

(4) The post-treated derivative is an alkenyl-substituted succinimide of formula (I) which is post-treated with boric acid, phosphoric acid, a carboxylic acid, or ethylene carbonate.

(5) The friction modifier is the friction modifier (B) and the dimer is prepared by dimerization of a linear α-olefin having 8 to 12 carbon atoms.

(6) The friction modifier is the friction modifier (B) and the dimer is 2-hexyl-1-decene, 2-octyl-1-dodecene or 2-decyl-1-tetradecene.

(7) The friction modifier is the friction modifier (B) and the dimer is 2-octyl-1-dodecene.

(8) The friction modifier is the friction modifier (B) and the alkylene-polyamine is ethylenediamine, diethylenetriamine or triethylenetetramine.

(9) The friction modifier is the friction modifier (B) and the alkylene-polyamine is diethylenetriamine. (10) The friction modifier is the friction modifier (B) and the post-treated derivative is the alkenyl-substituted succinimide of formula (II) which is post-treated with boric acid, phosphoric acid, a carboxylic acid or ethylene carbonate.

(11) The overbased sulfonate has a TBN in the range of 120 to 400 mg KOH/g (particularly, 260 to 400 mg KOH/g), and the overbased salicylate has a TBN in the range of 60 to 330 mg KOH/g (particularly, 150 to 250 mg KOH/g).

(12). The lubricating oil composition is for automatic transmissions.

(13) The lubricating oil composition is for automatic transmissions such as automatic transmissions, continuously variable transmissions, and dual clutch transmissions.

(14) The lubricating oil composition contains the friction modifier in an amount of 0.5 to 5 wt. % (preferably 1 to 4 wt. %, more preferably 1.5 to 3 wt. %) per the amount of the lubricating oil composition.

(15) The nitrogen-containing ashless dispersant contained in the lubricating oil composition is polyisobutenylsuccinimide or its post-treated compound.

(16) The post-treated compound is a borated polyisobutenylsuccinimide.

(17) The phosphorus compound contained in the lubricating oil composition is phosphoric acid, a phosphoric acid ester, phosphorous acid, a phosphorous acid ester, thiophosphoric acid, or a thiophosphoric acid ester.

(18) The lubricating oil composition contains an anti-oxidation agent.

(19) The lubricating oil composition contains a corrosion inhibitor.

(20) The lubricating oil composition contains a viscosity index improver.

(21) The base oil of the lubricating oil composition contains a saturated component in an amount of at least 90 wt. %, a viscosity index of 120 or more, and a sulfur content of 0.03 wt. % or less.

The friction modifier of the invention as well as the base oil and various additives comprised in the lubricating oil composition are described in more detail.

Friction Modifier

The friction modifier of the invention is an alkenyl-substituted succinimide represented by the aforementioned formula (1) or ((1) or its post-treated compound.

The alkenyl-substituted succinimide of the formula (1) can be prepared by reacting succinic anhydride substituted with a 2-alkenyl group having a branched structure in the the β-position with a polyamine.

The succinic anhydride substituted with a 2-alkenyl group having a branched structure in the β-position can be prepared by the reaction between succinic anhydride with an alkene compound having a vinylidene group at its terminal. The alkene compound having a vinylidene group at its terminal can be represented by the following formula (2):

In the formula (2), each of R₅ and R₆ is an aliphatic hydrocarbyl group (preferably a linear or branched alkyl group, more preferably a linear alkyl group) under such condition that a carbon atom number of R₅ is larger than a carbon atom number of R₆ by 3 or a carbon atom number of R₅ is smaller than a carbon atom number of R₆ by 1.

Examples of the alkene compound having a vinylidene group at its terminal include 2-hexyl-1-decene, 2-octyl-1-dodecene and 2-decyl-1-tetradecene. Each of these alkene compounds can be prepared by dimerizing 1-octene, 1-decene and 1-dodecene, respectively.

The above-mentioned alkene compounds having a vinylidene group at its terminal and their preparing methods are described in JP2006-225348 A and JP2006-232672 A.

Examples of the polyamines employable for the preparation of the alkenyl-substituted alkenylsuccinimide of the invention include ethylenediamine, diethylenetriamine and triethylenetetramine. Most preferred is diethylenetriamine.

The reaction between the succinic anhydride substituted with a 2-alkenyl group having a branched structure in the β-position and polyamine can be performed in the manner similar to the known manner for the reaction between succinic anhydride and polyamine.

The friction Modifier employed for the lubricating oil composition of the invention can be an alkenyl-substituted succinimide represented by the aforementioned formula (I) or (II) per se. Otherwise, the friction modifier can be a post-treated alkenyl-substituted succinimide which is obtained by post-treatment of the alkenyl-substituted succinimide with a known post-treating agent such as borate, phosphate, carboxylate or ethylene carbonate.

It should be noted that the reaction between the succinic anhydride substituted with a 2-alkenyl group having a branched structure in the β-position and polyamine may give a relatively small amount of a mono-type alkenyl-substituted succinimide of the following formula (III) in addition of the bis-type alkenyl-substituted succinimide of the formula (I) or (II):

In the formula (III), each of R₁, R₂, x and y has the aforementioned meaning, and each of R₃ and R₄ independently represents a hydrogen atom, an alkyl group having 1-12 carbon atoms, an aryl group having 6-12 carbon atoms, an aralkyl group having 7-13 carbon atoms, or a 5-8 membered heterocyclic group.

Therefore, the friction modifier of the invention may contain a small amount (20 wt. % or less) of the monotype alkenyl-substituted succinimide of the formula (III) in addition to the bis-type alkenyl-substituted succinimide of the formula (I) or (II).

Base Oil

There are no specific limitations with respect to the base oil to be employed for the preparation of the lubricating oil composition of the invention. For instance, base oils having various physical properties, for instance, base oils which are known for the conventional transmission oils or conventional engine oils for engines (particularly gasoline engines) of automobiles. Examples of the base oil include mineral oils belonging to Groups 1 to 3, synthetic oils belonging to Group 4, and other oils belonging to Group 5, which are described in API 1509. Preferred are mineral oils and synthetic oils containing a saturated component in an amount of at least 85 wt. % (more preferably, at least 90 wt. %) , a viscosity index of 100 or more (more preferably 120 or more), and a sulfur content of 0.03 wt. % or less (more preferably 0.001 wt. % or less).

The mineral-type base oil is preferably obtained by treating a distillate having a lubricating viscosity with known methods such as solvent refining and hydrogenation. Preferred are hyper-hydrogenated oil (i.e., hydrocracked oil which typically has a viscosity index of 120 or more, an evaporation loss (according to ASTM D5800) of 15 wt. % or less, a sulfur content of 0.001 wt. % or loss, and an aromatic content of 10 wt. % or less). A mixture of oils containing 10 wt. % or more of the hydrocracked oil is also employable. The hydrocracked oil can be an oil having a high viscosity index (e.g., a viscosity index of 140 or more, specifically a viscosity index in the range of 140 to 150) which is produced by isomerization or hydrocracking of a mineral type slack or natural gas, namely, gas-to-liquid (GTL) wax. The hydrocracked oil is preferably employable as a base oil of the lubrication oil composition of the invention due to its low sulfur content, low evaporating property and low carbonaceous residue.

The synthetic oil (synthetic lubricating base oil) can be poly-α-olefins produced by polymerization of α-olefin having 3 to 12 carbon atoms, dialkyl diesters prepared by esterification of di-basic acids (e.g., sebacic acid, azelaic acid, and adipic acid) with an alcohol having 4-18 carbon atoms, such as dioctyl sebacate, polyol esters prepared by esterification of mono-basic acids having 3 to 18 carbon atoms with 1-trimethylolpropane or pentaerythritol, or alkylbenzenes having an alkyl group of 9-14 carbon atoms. The synthetic oil is preferred as a base oil of the lubricating oil composition of the invention because not only it generally contains no sulfur-containing components but also it shows good oxidation resistance and good thermal resistance. Further, the synthetic oil gives less carbonaceous residues and less soots when it is burnt. Most preferred is poly-α-olefin.

The mineral base oil and synthetic base oil can be used singly or in combination such as combinations of two or more mineral base oils, combinations of two or more synthetic base oils, and combinations of mineral base oils and synthetic base oils in optional ratios.

Nitrogen-Containing Ashless Dispersant

Representative examples of the nitrogen-containing ashless dispersants employable for the preparation of the lubricating oil composition of the invention include alkenyl- or alkyl-succinimide of which alkenyl group or alkyl group is derived from polyolefin and its derivatives. A representative alkenyl- or alkyl-succinimide can be obtained by the reaction of succinic anhydride substituted with an alkenyl or alkyl group having a high molecular weight with a polyalkylene polyamine having 3-10 (preferably 4-7) nitrogen atoms per mole. The alkenyl or alkyl group having a high molecular weight preferably is polyolefin having an average molecular weight of approx. 900 to 5,000. Most preferred is polybutene.

In the process for preparing polybutenylsuccinic anhydride by the reaction of polybutene and maleic anhydride, the chlorination method employing chlorine can be employed. However, although the chlorination method gives the succinimide in a good yield, it generally results in the production of the succinimide containing a relatively large chlorine content (e.g., approx. 2,000 ppm). In contrast, the thermal method employing no chlorine can yields the succinimide containing an extremely small chlorine content (e.g., approx. 40 ppm or less). In addition, if a highly reactive polybutene (containing a methylvinylidene structure of approx. 50% or more) is employed in the thermal method in place of the conventional polybutene (mainly having β-olefinic structure), the reactivity of the thermal method increases. The increase of the reactivity is advantageous results in reduction of unreacted polybutene in the produced dispersant which favorably has an active component (succinimide) of an high concentration. Therefore, it is preferred that the polybutenylsuccinic anhydride is obtained by employing the high reactive polybutene in the thermal method, and that the resulting polybutenylsuccinic anhydride is reacted with a polyalkylene polyamine having an average nitrogen atoms of 3 to 10 (per one mole) to give a succinimide. The succinimide can be further reacted (or treated) with borate, an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, or an organic acid to give a modified succinimide. Particularly, borated alkenyl(or alkyl)succinimide is preferred because of its high thermal and oxidation resistance.

The succinimide can be of a mono-type, a bis-type or a poly-type, which corresponds to number of the imide structure in one molecule. In the lubricating oil composition of the invention, succinimides of bis-type and poly-type are preferably employed.

The nitrogen-containing ashless dispersant can be a polymer-containing succinimide which is prepared using an ethylene-α-olefin copolymer having a molecular weight in the range of 1,000 to 15,000, and an ashless dispersant of alkenylbenzylamine type.

Metal-Containing Detergent

The metal-containing detergent used in the lubricating oil composition of the invention preferably is a mixture of an overbased sulfonate having an alkyl group containing 20-24 carbon atoms and an overbased salicylate having an alkyl group containing 14-18 carbon atoms in a weight ratio of 1:4 to 4:1. The overbased sulfonate preferably has a TBN (Total Base Number) in the range of 120 to 400 mg KOH/g (more preferably, 260 to 400 mg KOH/g), and the over based salicylate preferably has a TBN in the range of 60 to 330 mg KOH/g (more preferably, 150 to 250 mg KOH/g).

The lubricating oil composition may further contain other metal-containing detergents such as over-based phenates and/or alkylcarboxylate having a variety of total base numbers, under such conditions that the total amount of other metal-containing detergents is less than the amount of the above-mentioned mixture of the sulfonate and salicylate.

Phosphorus Compound

The phosphorus compounds can be those which are known as anti-wear agents employable in the lubricating oil compositions. Examples of the phosphorus compound include phosphoric acid, a phosphoric acid ester, phosphorous acid, a phosphorous acid ester, thiophosphoric acid and a thiophosphoric acid ester. Also employable are amine salts of the phosphoric acid ester and phosphorous acid ester.

Oxidation Inhibitor

The lubricating oil composition of the invention can contain an oxidation inhibitor. The oxidation inhibitor preferably is a known inhibitor such as a phenolic oxidation inhibitor or an amine oxidation inhibitor. The oxidation inhibitor may be contained in the lubricating oil composition in an amount of 0.1 to 5 wt. %, preferably 0.5 to 3 wt. %.

The phenolic oxidation inhibitor can be a hindered phenol compound. The amine oxidation inhibitor can be a diarylamine compound.

Examples of the hindered phenol oxidation inhibitor include 2,6-di-t-butyl-p-cresol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-methylenebis(6-t-butyl-o-cresol), 4,4′-isopropylidenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2′-methylenebis(4-methyl-6-t-butylphenol), 4,4′-thiobis(2-methyl-6-t-butylphenol), 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and octyl 3-(5-t-butyl-4-hydroxy-3-methylphenyl)propionate.

Examples of the diarylamine oxidation inhibitor include a mixed alkyldiphenylamine having 4 to 9 carbon atoms, p,p′-dioctyldiphenylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylated α-naphthylamine and alkylated phenyl-α-naphthylamine.

The hindered phenol oxidation inhibitor and diarylamine oxidation inhibitor can be employed singly or in combination. If desired, other oil-soluble oxidation inhibitors can be employed in combination.

The lubricating oil composition of the invention can further contain other additives. Examples of other additives include a viscosity index improver (e.g., dispersant type viscosity improver or non-dispersant type viscosity improver), a corrosion inhibitor (e.g., a copper corrosion inhibitor such as thiazol compound, triazole compound, thiadiazole compound), a seal-swelling agent (e.g., an oil-soluble dialkylester of a dibasic acid such as adipic acid, azelaic acid, sebacic acid, or phthalic acid), a dye (e.g., red dye), a defoaming agent, and a pour-point depressant (e.g., polymethacrylic acid ester, polyacrylic acid ester, and polyacrylamide).

EXAMPLES

The present invention is further described by the following illustrative non-limiting working examples.

Synthesis Example 1 Synthesis of Friction Modifier According to the Invention (bis-type β-Branched Primary 2-alkenylsuccinimide)

2-Octyl-1-dodecene (1 mol), maleic anhydride (1 mol) and 2,2-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (oxidation inhibitor, 0.003 mol) were mixed, and the mixture was reacted at 200° C. for 4 hours, to give a primary alkenylsuccinic anhydride. To the alkenylsuccinic anhydride (1 mol) was added diethylene triamine (0.5 mol). The mixture was reacted at 160° C. for 2 hours and subsequently dried under reduced pressure for 30 minutes to yield a reaction product. By IR spectroscopy, it was confirmed that the reaction product was the desired bis-type β-branched primary 2-alkenylsuccinimide (product comprising two alkenylsuccinimide moieties bridged with a diethylenetriamine residue, nitrogen content: 4.9 wt. %).

Synthesis Example 2 Synthesis of Friction Modifier According to the Invention (bis-type β-Branched Primary 2-alkenylsuccinimide)

The procedures of Synthesis Example 1 were repeated except for replacing diethylenetriamine with triethylenetetramine, to yield the desired bis-type β-branched primary 2-alkenylsuccinimide (reaction product comprising two alkenylsuceinimide moieties bridged with a triethylenetetramine residue).

Synthesis Comparative Example 3 Synthesis of Friction Modifier for Comparison (bis-type α-Branched Secondary 2-alkenylsuccinimide)

To isooctadecenylsuccinic anhydride (prepared by the reaction of maleic anhydride with octadecene produced by isomerization (internal olefination) of linear 1-octadecene, 1 mol) was added diethylenetriamine (0.5 mol). The resulting mixture was reacted at 160° C. for 2 hours, and subsequently dried under reduced pressure for 30 minutes, to give a reaction product. By IR spectroscopy, it was confirmed that the reaction product was the desired bis-type α-branched secondary 2-alkenylsuccinimide (nitrogen content: 5.2 wt. %).

Examples, Reference Examples and Comparison Examples —Preparation of Lubricating Oil Composition—

The lubricating oil composition was prepared by adding the below-described nitrogen-containing ashless dispersant, friction modifier, metal-containing detergent, oxidation inhibitor, corrosion inhibitor, phosphorus compound, viscosity index improver, pour point depressant, seal-swelling agent and defoaming agent in the below-described amounts to the below-described base oil in the below-described amount.

-   (1) Base oil (79.50 wt. %)

Paraffinic hyper purified mineral oil

-   (2) Nitrogen-containing ashless dispersant (3.80 wt. %)

Borated polyisobutenylsuccinicimide

-   (3) Friction modifier 1 (2.50 wt. %)

Friction modifier prepared in the aforementioned Synthesis Example 1 for Examples 1 and 2

Friction modifier prepared in the aforementioned Synthesis Example 2 for Examples 3 and 4

Friction modifier prepared in the aforementioned Synthesis Example 3 for Reference Example

-   (4) Friction modifier 2 (0.20 wt. %)

A mixture of a conventional amine-type friction modifier and a conventional ester-type friction modifier

-   (5) Metal-containing detergent (0.60 wt. %)

A mixture (1/1 by weight) of the following overbased sulfonate and overbased salicylate

Overbased sulfonate having an alkyl group containing 20 to 24 carbon atoms and a TBN of approx. 300 mg KOH/g

Overbased salicylate having an alkyl group containing 14 to 18 carbon atoms and a TBN of approx. 200 mg KOH/g

-   (6) Oxidation inhibitor (1.20 wt. %)

A mixture of an amine-type oxidation inhibitor and a phenol-type oxidation inhibitor

-   (7) Corrosion inhibitor (0.07 wt. %)

A mixture of a thiadiazol-type corrosion inhibitor and a benzotriazole-type corrosion inhibitor

-   (8) Phosphorus compound (0.30 wt. %)

Alkyl Phosphite

-   (9) Viscosity index improver (11.00 wt. %)

A dispersant-type polymethacrylate viscosity index improver

-   (10) Pour-point depressant (0.20 wt. %)

A polymethacrylate-type pour-point depressant

-   (11) Seal-swelling agent (0.60 wt. %)

A sulforane-type seal-swelling agent

-   (12) Defoamer

A silicon-type defoamer

—Lubricating Oil Composition for Comparison—

Two commercially available transmission oils (CVTF, Comparison Oil A and Comparison Oil B) were purchased for comparison.

—Evaluation Method for Lubricating Oil Composition— (1) Determination of Friction Coefficient

The friction coefficient was determined in terms of a metal-metal friction coefficient by means of a block-on-ring tester according to “Standard test method for metal on metal friction characteristics of belt CVT fluids” described in JASO M358:2005. Details of the testing method are described below.

-   -   Testing conditions         -   Ring: Falex S-10 Test Ring (SAE 4620 Steel)         -   Block: Falex H-60 TEst Block (SAE 01 Steel)     -   Amount of oil         -   150 mL     -   Break-in Conditions         -   Oil temperature: 110° C.         -   Load: 5 min. under 890 N and 25 min. under 1112 N         -   Sliding velocity: 5 min. at 0.5 m/s—25 min. at 1.0 m/s     -   Testing Conditions         -   Oil temperature: 110° C.         -   Load: 1112 N         -   Sliding velocity: 5 min. each at 1.0, 0:5, 0.25, 0.125,             0.075, 0.025 m/s         -   Friction coefficient: a friction coefficient for 30 sec.             before the change of the sliding velocity

(2) Determination of Anti-Shudder Performance Durability

The anti-shudder performance durability was determined by means of a low velocity friction apparatus according to “Road vehicles—Test method for anti-shudder performance of automatic transmission fluids” described in JASO M-349:2001. Details of the testing method are described below.

-   -   Testing conditions         -   Friction material: cellulose disc/steel plate

2Amount of oil: 150 mL

-   -   Break-in conditions         -   Contact pressure: 1 MPa         -   Oil temperature: 80° C.         -   Sliding velocity: 0.6 m/s         -   Sliding time: 30 minutes     -   □V Performance test conditions         -   Contact pressure: 1 MPa

2Oil temperature: 40, 80, 120° C.

-   -   -   Sliding velocity: continuously increasing and decreasing             between 0 m/s to 1.5 m/s

    -   Durability test conditions         -   Contact pressure: 1 MPa         -   Oil temperature: 120° C.         -   Sliding rate: 0.9 m/s         -   Time: 30 minutes         -   Rest time: 1 minute         -   Performance measurement time: μ-V characteristics was             measured every 24 hour from 0 hour

Note: The anti-shudder performance was evaluated by determining a period of time until μd/dV at 0.9 m/s reached 0. The longer the determined period of time is, the better the anti-shudder performance is.

—Results of Evaluation of Lubricating Oil Composition—

The friction coefficient and anti-shudder durability determined for each lubricating oil arc set forth in Tables 1 and 2.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Friction Syn. Ex. 1 Syn. Ex. 2 Modifier 2.5 wt. % 1.5 wt. % 2.5 wt. % 1.5 wt. % Friction coefficient    1 m/s 0.084 0.097 0.096 0.103  0.5 m/s 0.114 0.114 0.116 0.117  0.25 m/s 0.128 0.129 0.127 0.129 0.125 m/s 0.137 0.135 0.134 0.134 0.075 m/s 0.140 0.139 0.137 0.138 0.025 m/s 0.144 0.141 0.140 0.141 Average friction 0.125 0.126 0.125 0.127 coefficient Anti-shudder durability 504 288 288 264 (hours)

TABLE 2 Ref. Example Com. Oil A Com. Oil B Friction Syn. Ex. 3 Unknown Modifier 2.5 wt. % Unknown Friction coefficient    1 m/s 0.072 0.077 0.085  0.5 m/s 0.098 0.102 0.105  0.25 m/s 0.117 0.123 0.118 0.125 m/s 0.129 0.133 0.125 0.075 m/s 0.134 0.137 0.128 0.025 m/s 0.139 0.141 0.138 Average friction coefficient 0.115 0.119 0.117 Anti-shudder durability 456 192 96 (hours)

Evaluation

As is apparent from the friction coefficient at each sliding rate, each of the lubricating oil compositions of Examples 1 to 4 containing the new friction modifier gives a high friction coefficient at each sliding velocity which less varies in the range of 1 m/s to 0.025 m/s, and gives a high average friction coefficient. Moreover, the lubricating oil compositions of Examples 1 to 4 show sufficiently long anti-shudder duration.

In contrast, the commercially available CVTF (Corn. Oil A) gives a relatively low friction coefficient and shows a relatively short anti-shudder duration. The commercially available CVTF (Com. Oil B) also gives a relatively low friction coefficient and shows a further shorter anti-shudder duration.

The lubricating oil composition of Comparison Example which contained the friction modifier prepared in Synthesis Example 3 shows a long anti-shudder duration but gives a relatively low friction coefficient.

Accordingly, it is apparent that the lubricating oil composition containing a friction modifier of the present invention shows excellent performances, particularly as transmission oil. 

1. A lubricating oil composition comprising a base oil having a lubricating viscosity and the following additives: a friction modifier in an amount of 0.1 to 10 wt. %, a nitrogen-containing ashless dispersant in an amount of 0.05 to 10 wt. %, a phosphorus compound in an amount of 0.1 to 10 wt. %, and a metal-containing detergent in an amount of 0.005 to 4 wt. %, in which the amounts of the additives are based on an amount of the lubricating oil composition, the friction modifier is selected from the group consisting of: a friction modifier (A) comprising an alkenyl-substituted succinimide of the following formula (1) or a post-treated derivative thereof:

in which each of R₁ and R₁′ independently is an alkenyl group having a branched structure in β-position which is represented by the following formula (1), R₂ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 13 carbon atoms, or a 5-8 membered heterocyclic group, x is an integer of 1 to 6, and y is an integer of 0 to 20:

in which each of R₃ and R₄ is an aliphatic hydrocarbyl group and a total carbon atom number of R₃ an R₄ is in the range of 3 to 45, under the condition that a carbon atom number of R₃ is larger than a carbon atom number of R₄ by 3 or a carbon atom number of R₃ is smaller than a carbon atom number of R₄ by 1; and, a friction modifier (B) which comprises an alkenyl-substituted succinimide of the following formula (II) or a post-treated derivative thereof:

in which each of R₁ and R₁′ independently is an alkenyl group having a branched structure in β-position which is derived from a dimer of a single linear α-olefin having 3 to 24 carbon atoms, and Q is a residue of an alkylene-polyamine having a 1 to 20 carbon atoms and containing an amino group at least at each terminal thereof, and said metal-containing detergent is a mixture of an overbased sulfonate having an alkyl group containing 20-24 carbon atoms and an overbased salicylate having an alkyl group containing 14-18 carbon atoms in a weight ratio of 1:4 to 4:1.
 2. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (A) in which each of R₃ and R₄ in the formula (1) independently is a linear alkyl group and the total carbon atom number contained in R₃ and R₄ is in the range of 13 to
 21. 3. The lubricating oil composition of claim 1, in which x is 2 and y is an integer of 1 to
 3. 4. The lubricating oil composition of claim 1, in which x is 2 and y is
 1. 5. The lubricating oil composition of claim 1, in which the post-treated derivative is an alkenyl-substituted succinimide of formula (1) which is post-treated with boric acid, phosphoric acid, a carboxylic acid, or ethylene carbonate.
 6. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (B) wherein the dimer is prepared by dimerization of a linear α-olefin having 8 to 12 carbon atoms.
 7. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (B) wherein the dimer is 2-hexyl-1-decene, 2-octyl-1-dodecene or 2-decyl-1-tetradecene.
 8. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (B) wherein the dimer is 2-octyl-1-dodecene.
 9. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (B) wherein the alkylene-polyamine is ethylenediamine, diethylenetriamine or triethylenetetramine.
 10. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (B) wherein the alkylene-polyamine is diethylenetriamine.
 11. The lubricating oil composition of claim 1, in which the friction modifier is the friction modifier (B) wherein the post-treated derivative is the alkenyl-substituted succinimide of formula (II) which is post-treated with boric acid, phosphoric acid, a carboxylic acid or ethylene carbonate.
 12. The lubricating oil composition of claim 1, in which the overbased sulfonate has a TBN in the range of 120 to 400 mg KOH/g and the overbased salicylate has a TBN in the range of 60 to 330 mg KOH/g.
 13. The lubricating oil composition of claim 1, which is a lubricating oil for automatic transmissions.
 14. The lubricating oil composition of claim 13, in which the automatic transmissions are selected from the group consisting of automatic transmissions, continuously variable transmissions and dual clutch transmissions.
 15. A method for operating an automatic transmission in the presence of the lubricating oil composition of claim
 1. 16. The method of claim 15, in which the automatic transmission is selected from the group consisting of automatic transmissions, continuously variable transmissions and dual clutch transmissions. 